ELECTRIC LINEAR DICHROISM AS A NEW TOOL TO STUDY SEQUENCE PREFERENCE IN DRUG-BINDING TO DNA

An original approach using electric linear dichroism (ELD) and natural DNAs and polynucleotides of differing base composition has been devel oped with the aim to investigate the sequence-dependent recognition of DNA by drugs. Both intercalators and minor groove binders have been s tudied as well as certain hybrid molecules. The results indicate that the orientation of drugs upon binding to nucleic acids can change mark edly according to the target sequence, Among the intercalators tested, only actinomycin D and hycanthone show a clear preference for GC- and AT-rich sequences, respectively. For minor groove binders, the linear dichroism showing a strong dependence on base composition of the DNA and polynucleotides is most pronounced. Netropsin and distamycin bind to DNA with a marked AT specificity. Hoechst 33258, berenil and DAPI e xhibit positive and negative dichroism signals at AT and GC sites resp ectively, suggesting that at least two types of drug-DNA interaction a re involved depending on the AT/GC content of the DNA. Further investi gations using polynucleotides with inosine substituted for guanosine, and competition experiments with intercalative drugs suggest that Hoec hst 33258, berenil and DAPI interact with GC sequences via a non-class ical intercalation process.